Astronomy: Galaxies and the Universe
Exploring galaxy types, cosmic distances, and the expanding universe
Astronomy: Galaxies and the Universe
Exploring galaxy types, cosmic distances, and the expanding universe
Astronomy - Grade 6-8
- 1
A galaxy contains billions of stars, along with gas, dust, and dark matter. Explain why gravity is important in a galaxy.
Think about the force that keeps objects attracted to one another.
Gravity is important because it pulls stars, gas, dust, and dark matter together and helps hold the galaxy in its shape. - 2
Name the three main types of galaxies and briefly describe one feature of each type.
The three main types of galaxies are spiral, elliptical, and irregular. Spiral galaxies have arms that wind outward, elliptical galaxies are rounded or stretched like ovals, and irregular galaxies do not have a clear regular shape. - 3
The Milky Way is a barred spiral galaxy. What does this mean about its shape?
Focus on the words barred and spiral.
It means the Milky Way has a spiral shape with arms and also has a bar-shaped structure of stars across its center. - 4
A light-year is the distance light travels in one year. Explain why astronomers use light-years instead of kilometers to describe distances between galaxies.
Astronomers use light-years because distances between galaxies are extremely large, and light-years make those distances easier to describe and compare than very large numbers of kilometers. - 5
Light from a galaxy takes 2 million years to reach Earth. How far away is the galaxy, and what does this tell us about the image we see?
One light-year is the distance light travels in one year.
The galaxy is 2 million light-years away. The image we see shows the galaxy as it looked 2 million years ago because its light took that long to reach us. - 6
Describe one difference between a star cluster and a galaxy.
A star cluster is a group of stars held together by gravity, but a galaxy is much larger and contains billions of stars, gas, dust, and dark matter. - 7
Scientists observe that most distant galaxies are moving away from us. What does this evidence suggest about the universe?
Think about what happens when dots on a balloon move apart as the balloon inflates.
This evidence suggests that the universe is expanding, meaning space itself is stretching and galaxies are getting farther apart over time. - 8
What is redshift, and how does it help astronomers study galaxies?
Redshift is the stretching of light waves toward longer, redder wavelengths. It helps astronomers tell that many galaxies are moving away from us and helps them study the expansion of the universe. - 9
The Andromeda Galaxy is about 2.5 million light-years away. If its light reaches Earth tonight, when did that light leave Andromeda?
The number of light-years tells how many years the light traveled.
The light left Andromeda about 2.5 million years ago because it took 2.5 million years to travel to Earth. - 10
Put these objects in order from smallest to largest: solar system, planet, galaxy, universe.
The correct order from smallest to largest is planet, solar system, galaxy, universe. A planet is part of a solar system, a solar system is part of a galaxy, and galaxies are part of the universe. - 11
A telescope observes a galaxy with no clear spiral arms and a smooth oval shape. What type of galaxy is it most likely to be? Explain your answer.
Match the description to the galaxy shape.
It is most likely an elliptical galaxy because elliptical galaxies usually have smooth oval or round shapes and do not have clear spiral arms. - 12
Explain why looking at very distant galaxies is like looking back in time.
Looking at very distant galaxies is like looking back in time because their light takes millions or billions of years to reach Earth. We see them as they were when the light began traveling, not exactly as they are today.